The exotic fauna of Siarau's swamps

A beautiful, penetrating wildlife film slips quietly into place as the second of the dependably excellent new National Geographic specials. Although accomplished with the sanction of the Brunei government, Creatures of the Mangrove (PBS, tonight, 8-9 p.m., check local listings) appears to cause little upheaval in the environment as its expert cinematographers sneak onto the tiny island of Siarau off the north coast of Borneo for a day and nighttime peek at some of the oddest creatures on the face of the earth. Siarau has a tidal forest of mangrove trees, caught between land and sea, protected by ``the great patriarch'' of the rain forest above.

Photographers Jim Clare, Richard Foster, and Mike Potts, under the aegis of producer Phil Agland with a grant from Chevron Corporation, have brought back incisive footage of the flora-fauna relationship, with breathtaking slow-motion and stop-motion photography. Viewers will see the red-faced, pot-bellied, bulbous-nosed proboscis monkey stalking comically but majestically through the swamps. There is fascinating footage of fiddler crabs, mudskippers, cat snakes, crab-eating frogs, mud lobsters, fruit bats, moth caterpillars, and tiny mouse deer.

The film is a prime example of complex ecological interdependence as it has seldom, if ever, been recorded. The script is delivered with reverence by Richard Kiley; the imaginative music track was written and performed by Jennie Muskett.

As befits a high-minded National Geographic special, attention is called to the dangers to similar ecosystems in the world, many of which are in the process of being destroyed, although Borneo's Siarau seems still to be safe. But, our narrator intones, ``if the rain forests are allowed to disappear, the mangroves will suffocate and life in the mangrove forests will vanish. . . .''

The ecosystem described in ``Creatures of the Mangrove,'' according to the National Geographic, is a kind of ``microcosm for mankind. This world awaits its fate.''